One type of continuously variable transmission (CVT) for automotive vehicles includes, for example: a drive pulley disposed on an engine side; a driven pulley disposed on a drive-wheel side; and an endless-belt-like chain entrained between these pulleys. One type of the power transmission chain includes: a plurality of links; and a plurality of pins for interconnecting these links. Such a continuously variable transmission of a so-called chain type transmits power by way of traction produced from contact friction force between sheave surfaces and end faces of the pins of the chain, the sheave surfaces defined by two conical surfaces disposed internally of each pulley as substantially opposed each other. An alternative continuously variable transmission has an arrangement wherein chain friction transmission members, as a separate member from the pin, are arranged along a chain longitudinal direction at predetermined space intervals, such that power may be transmitted by way of traction produced from the contact friction force between the opposite end faces of the chain friction transmission members and the sheave surfaces. Furthermore, a distance (groove width) between the conical sheave surfaces of each of the drive pulley and the driven pulley is continuously varied for continuously varying an effective radius of each pulley. As a result, speed change ratio is continuously varied (infinitely variable). Thus is provided smooth gearless shift transmission, which is not provided by a conventional gear-type transmission.
In such a chain-type continuously variable transmission, uncomfortable noises are produced when the pins or the like of the entrained chain approach the sheave surfaces of each pulley or when the pins or the like leave the sheave surfaces. Particularly when the pins approach the sheave surfaces, the pins collide with the sheave surfaces to produce the noises. A plurality of pins are arranged along the chain longitudinal direction with a predetermined pitch and hence, these pins sequentially collide with the sheave surfaces to produce the noises.
Since a normal chain includes the plural pins having the same length, all the pins collide with the sheave surfaces the same way. Accordingly, the noises resulting from the collision of the individual pins substantially have the same frequency, so that the noise at this frequency is increased to raise a sound pressure level. In this connection, Japanese Unexamined Patent Publication No.S63(1988)-53337 discloses an invention wherein a plurality of pins having different lengths are used for dispersing the frequencies of the produced noises or suppressing resonance, thereby lowering the sound pressure level.
On the other hand, Japanese Unexamined Patent Publication No.H8(1996)-312725 discloses a power transmission chain for use in continuously variable transmission. The chain includes: a plurality of links each possessing first and second through-holes arranged in the chain longitudinal direction; and a plurality of pins and a plurality of inter-pieces, each of which pins and inter-pieces penetrates the first through-hole of one link and the second through-hole of the other link thereby interconnecting the links, adjoining in a chain widthwise direction, in a manner to provide bending in the chain longitudinal direction; and is arranged such that the pin fixed in the first through-hole of the one link and movably fitted in the second through-hole of the other link and the inter-piece movably fitted in the first through-hole of the one link and fixed in the second through-hole of the other link are brought into relative movement in rolling contact thereby permitting the bending of the chain, and that an involute of a circle defines a sectional shape a contact portion of a pin side surface, at which the pin contacts the inter-piece.